Method of developing oil fields



166-25U FIPROli Ill Peseta a, 1931 i unit-en s'rarasrarainr osrica ma L.DOHERTY, or new roan, x. Y.

unrnon or nnvnnornvc on. rmns R0 Drawing. Application filed-11111 20,1925, Serial No. 44,915. Renewed Kay 20, 1980.

This invention relates to the development of oil fields and moreparticularly to a method of extracting the oil from the oil bearingsands in such a manner that the expulsive force of the gas usually foundwith the oil may be utilized to the best advanta e in extracting the oilfrom the sands and ringing it to the surface.

Unless an oil pool iscontrolled by a single operator, the wells areusually projected into.

the oil sands in a more or less haphazard manner without any particularregard to the character of the oil sands and the other factors governingoil production, each operatpr striving to be the first to get producingwells into the oil sands in order to profit by the flush productionwhich usually follows when the wells are first, entered into theproducing sands. In other words, no particular system of control ofthewells is practiced, each well being allowed to flow from the time it isentered in the oil bearing sands. Where a single operator has control ofan oil pool, the method of oil production is not substantially differentfrom that where more than one operator is entitled to enter the field,the

primary difierence being that not so many wells will be sunk in thefield. -Ho\ vever, such wells as are sunk in the field are allowed toflow from the time the oil bearing sands have been reached withoutregard to other wells which may subsequently be drilled into the samesands. As a consequence the percentage of oil recovered from the sandsby present methods of oil production falls far short of the percentagewhich might be recovered if the expulsive force of the gas could befully utilized.

When a single well is first opened to the flow of oil andgas there isroduced an exccssive amount of gas which 18 due primarily to the factthat gas travels more readily than oil over a large area to a point ofdecreased pressure; As a result of the excessive production of gas thegas pressure over the entire oil area or horizon declines more rapidlythan the amount of oil produced .would warrant.

I have devised a method of. flowing 011 from the oi. sends constitutingthe oil pool 'ity of each well.

some of the wells may reach the oil produc-' ing sands ahead of othersin which event such wells will be shut in for the time being or unt1lall of the wells have-reached the oil producing sands after which theentire group of wells will be opened simultaneously and allowed to flowoil and gas. By developing the field as I propose, that is to say, byopening all of the wells simultaneously, the gas pressure will beexerted on all of the wells and will result in a much greater oilproduction becauseneither the oil nor gas will have to travel anexcessive distance to-the well which is the point of decreasedpressureand consequently-the energy of the gas over the field and withinthe gas will be utilized to best advantage in moving oil to the well.The oil in its natural condition in the sand contains-a large quantityof dissolved gas. the amount of gas dissolved in the oil depending onthe rock pressure. As set forth in a pending application I havediscovered that oil containing natural gas-in solution has a much lowerviscosity than oil which contains nodissolved gas. It therefore followsthat the oil in its natural condition is more mobile or fluid than isthe case when the gas ress'ure has been released and the dissolv'a gasescaped from the oil. Other conditions being equal the force required tomofii a'viscons liquid through capillary openings such as those whichexist in an oil sand varies diicctly with the Viscosity of the fluid.

While the wells are producing, there will be an area of decreasedpressure in the vicin- When the wells haw; been producing until thepressure has fallen to a certain point it is proposed to shut-in all theobtained than when they were shut in and this increased production willapply to all of the wells operating in the field. lVhen m the wells areclosed in for the purpose of allowing equalization of pressure to takeplace some of the gas more particularly that which exists in thevicinity of the well where the pressure is low, will be forced back intosolution under the increase of pressure.

v It ispreferred to operate the wells under a controlled back pressureso that excessive quantities of gas will not be produced with theoil,the ideal condition being such that thevolume of as produced witheach barrel of oil would lie equivalent to the gas dissolved in the oilunder naturally occurring.

conditions.

In orderto prevent the ress ure on the field from declining too ra id yit is desirable to returnto the OllSSJld t e natural gas which is beingproduced with the oil. When the wells are operated under a backpressure, the pressure of the outcoming gas will be comparatively highand it will, therefore, be a comparatively s mple matter to increase orboost the pressure of such gas sufficiently to enable it to be forced orinjected into the oil sands. I

v Additional gas taken from nearby fields can also be introduced intothe sands while the wells are producing and after they are shut in toenable the pressure on the field to be brought up to the desired pointwhich may be greater or less than the'natural rock pressure. If naturalgas is not available air may be used for the same purpose.

the flow of oil tends to decrease quite rapidly and the pressure dropsvery rapidly after afield has been producing efor sometime, theeeonomiccost of pumping gas may be so high that it will not be advisable to pumpinto the producing sand sufiicient gas to raise the oil to the originalrock pressure. Under such conditions the pressure would be be raised byintroducing gas only to a point suf- -ficient to hold a desirableviscosity of the oil and to maintainthe production. A gradual drop inpressure can be continued until all of the oil has been removed that iscapable of being removed by flowing under. the pres sure of the oil andgas in the sand- The back ressure which should be kept on the wells willdepend upon various factors among which may be mentioned the porosity soof the sands in which the oil and gas occur. In order to determine whatback pressure should be maintained samples of the sands will be obtainedand these samples subjected to laboratory tests to determine among other85 things the rate of migration of the oil and gas through the sandsunder pressures approximatil-ig. those in the oilfield and whatdifferential pressure should be maintained to produce the proper flowofoil, the tests being made with samples of oil and gas taken from thesame field. The cores of the bores taken from the oil sand should bewatched very carefully to be sure that the well opens into the mostorder to give t 1e oil the advantage of migration through the most orousportion.

Another factor which has an important bearingon the back pressure whichshould be kept u )onthe wells is the extent of reduction o .the pressurewhich must be given in order to set free the potential energy of the gasin the oil. This pressure reduction preferably should be made assuddenly as possible in order to start a movement or etfervescence ofthe gas in the oil. This efiervescence or boiling of the gas tends toconvert the orous portion of the sand in oil into a foamy mass and carrythe oil as foam toward the outlets of the well. If the pressure isreduced gradually the gas will come out of the oil without mucheffervescence. It is desirable therefore that the pressure changesshould be manipulated so-that as much etfervescing or bubbling of theoil can be obtained as possible. This eifervescnce should take plaw notonly at the opening ofthe well but back through the sands as far aspracticable. Where there are a large numberof openings an subject to thesame pressure, the foamy oily mass has a better op ortum'ty to reach apoint of low pressure. e

back pressure is maintained at the-top of the well to prevent waste andto conserve the energy of the gas and oil. The highest 3- sible backressure should be maintain at the top of t o well in order to mcover gasat high pressure so that this high pressure 5 may be returned to the oilsands. The big or the pressure of the gas recovered at the easing heedthe less power will be required in compressing itin order to raise itspres sure sufficiently high to force it back into the sand. Accordinglythe. pressure at the easing head may be reduced to substantiallyatmospheric pressure at the time the wells are opened, in order to startthe eilervescence or the sudden release of the gas from the 011 Hill andthen the back premure may be built up as the other wells or are shut inalto ethen Furthermore if some of the wells shoul cease flowing oil suchwells would be shut in.

In addition toll-1e gas which goes back into solution in the oil onaccountof the equalization of pressure, the increased pressureresultting from forcinggas into the sands will cause additional volumesof gas to go into solution in-the oil and thereby further increase itsfluidity. Also there is obtained a greatcr,expulsivc force when the oilwellsare again opened due to the increased pressure in the vicinityof'the wells.

From the foregoing description it will lie .readily appreciated that asimple and practical method of producing oil is provided,-

' a. method which enables the. pressure of the gas on-the field to beutilized in a n2c-t efiective manner in the production of oil.

What is claimed is:

1 A method of'developing an oil field comprising projecting a pluralityof wells into an oil sand, preventing flow of gas and oil from any givenwell until all of the wells are ready for producingand then flowing theoil and gas from all the wells simultaneously.

2. A method of developing an oilfield comprising projecting a pluralityof wells into an oil sand, preventing flow of gas and oil from any givenwell until all of the wells are ready for producing and then flowing theoil and gas from substantially all the wells simultaneously under ahack-pressure.

3. Inthe method of claim 2 the steps of opera ting oil wells under auniform backpressure and periodically reducing the pressure qually onall of the wells simultaneously. 4. 'A method of developing an oil fieldcoinprising projecting a plurality of wells into an oil sand, preventingflow of gas and. oil. from any given well until all of the wells areready i'or producing, then flowing the oil and gas from substantiallyall thewells simultaneously, and shutting in any well .whichsubsequently flows more gas than other wells. 5. In the method of claim1 the steps com prising allowing 'all of the wells to flow oiland gasuntil the gas pressure falls to a-predetermined point, thereaftershutting in all of the wells until theprc-ssure remaining inthe sandshas equalized over the entire lield,

and again opening the wells.

6. In'thc method of claim 1 the steps comprising allowing all of thewells to flow oil and gas until the as pressure falls toa predeterminedmint. thereafter shuttim in all of the wells and restoring pressure overthe entire oil area by injecting a gaseous fluid into the oil sands." v

7. A method of developing an oil field comprising projecting a pluralityof wells into an oil sand, allowing all of the wells to flow oil and gas"under a back-pressure until the gas pressure falls to apredetermi-nedpoint and then shutting in the wells, pumping a gaseousfluid into the held to bring the pressure in the oil sands up to a.predetermined simultaneously.

8; A method of dcvelopin an oil liehl.

.point, and again opening all o l the wells comprising projectin aplurality of Wcllsjnto an oil sand and a lowing all. of the wellsnatural gas coming from the flowing wells, shutting in the wells whenthe gas pressure falls to a predetermined point, pumping into the field.a gaseous fluid under pressure until to flow oil'and gas,.restoring tothe field the the pressure in the field has reached a prcdetermined-poiat, and the wells.

9. In the method of claim- 2, the steps of maintaining suchback-pressure on the wells a ain 0 nin all of that substantially thesame ratio between oil and gas flowing from the wells is maintained atall of the wells. r c

10. A method of developing an oil field comprising projecting aplurality of wells into an 011 sand, maintaining such back-pressure' onthe wells that an antiallylhe same ratio between oil and gas flowingfromthe well is maintained at all of the wells, and

shutting in such wells as produce an excess ofgas. 11. maintaining suchback pressure on the well thatsnhstantially the same production ratiobetween oil and gas is maintained 'at all of the wells, shutting in thewells when the gas pressure reaches a predetermined point and allowingthpressure in thefiel; to equalize;

. 12.- In the method of claim '2, the steps of maintaining such backpressure on each of the wells thatsubstantially the same productionratio between oiland gas is maintained at all of the wells, shutting insuch 'wells'as produce an excess amount of gas, and increasing thepressure in the oil sands by pumping a gaseous fluid, into the field.-

13. In the method of claim 2,- the steps of In the method 0t claim 2,the steps of maintaining a controlled back-pre sure on the wells suchthat a definite Ill-()(hlCLiJll ratio between oil and gas is maintainedat each of the wells, restoringtothe field the natural gas flowing fromthe wells, and shutting in any well which produces an excess quantity ofit. A method of develo aing an oil field III! comprising projecting aurality of wells into an oil sand, maintaining such hack-pres ,sure oneach of-the wells that a substantially duction ratio between oil and gasis main: ta'ined at all of the wells, restoring to the field the naturalgas flowing from the wells, Shutting in any well which produces anexcess quantity of gas, finally shuttin'g in all of the wells,increasing the pressure over the entire field lay-pumping into the samea gaseous fluid under pressure, and thereafter opening all of v thewells andallowing them to flow under a back-pressure. r 16. A methodpfdeveloping a new oil field comprising pro ecting a plurality of wellsinto an oil bearing sand, opening the wells to the flow of oil and gas;allowing the wells to flow until more gas is flowing than wouldordinarily flow if only that gas which is dissolved in the oilconstitute the expulsive force, shutting in the wells, increasing thegas pressure in the fieldsufiiciently to redissolve the natural gas inthe oil in the oil sand, and thereafter opening the wells simultaneouslyto the further flow of oil and gas.

17. A methodofdevelopinga new oil field comprising pro ecting a.plurality of wells into an oil sand in spaced relation throughoutsubstantially the entire oil sand area,

preventing flow of oil from any of the wells until all the wells areready for production,-

and opening all of the wells simultaneously 'to the flow of oil and gas.

In testimony, whereof I afiix m signature. HENRY L. DOfiERTYL

